1. Field of the Invention
This invention relates in general to color photography and in particular to new and improved color developing compositions and processes for forming photographic color images. More specifically, this invention relates to color development with a color developing composition containing a primary aromatic amino color developing agent and an anti-oxidant which serves to protect the developing agent against aerial oxidation.
2. Description of the Prior Art
The formation of color photographic images by the image-wise coupling of oxidized primary aromatic amino developing agents with color forming or coupling compounds to form indoaniline, indophenol, and azomethine dyes is well known. In these processes, the subtractive process of color formation is ordinarily used and the image dyes customarily formed are cyan, magenta, and yellow, the colors that are complementary to the primary colors, red, green, and blue, respectively. Usually, phenol or naphthol couplers are used to form the cyan dye image; pyrazolone or cyanoacetyl derivative couplers are used to form the magenta dye image; and acylacetamide couplers are used to form the yellow dye image.
In these color photographic systems, the color-forming coupler may be either in the developer solution or incorporated in the light-sensitive photographic emulsion layer so that, during development, it is available in the emulsion layer to react with the color developing agent that is oxidized by silver image development. Diffusible couplers are used in color developer solutions. Nondiffusing couplers are incorporated in photographic emulsion layers. When the dye image formed is to be used in situ, couplers are selected which form nondiffusing dyes. For image transfer color processes, couplers are used which will produce diffusible dyes capable of being mordanted or fixed in the receiving sheet.
It is common practice in the photographic art to include a sulfite in color developer compositions containing primary aromatic amino color developing agents. Typically, the sulfite utilized is in the form of an alkali metal sulfite or bisulfite. It is employed for the purpose of retarding aerial oxidation of the primary aromatic amino color developing agent and is generally quite effective for this purpose. However, the amount of sulfite which can be tolerated in the developer solution is limited by the fact that sulfite competes with couplers for oxidized developing agent and thereby adversely affects dye formation. Typically, yellow-dye-forming couplers react with oxidized developing agent more slowly than cyan-dye-forming couplers or magenta-dye-forming couplers so that the competition between coupler and sulfite has the greatest adverse effect on the formation of the yellow dye image.
Current trends in photographic processing favor lower replenishment rates in color processes, and these have presented problems associated with lower turnover rates and higher concentrations of replenisher ingredients. Lower turnover rates result in longer residence time for solutions in the processor. This produces greater aerial oxidation of the developing agent. This tendency can be counteracted by increasing the concentration of sulfite in the developer solution but, in turn, this results in adverse effects on the dye images, especially a lowering of yellow shoulder and yellow D.sub.max, because of the fact that sulfite competes with couplers for oxidized developing agent. Thus, if the amount of sulfite is kept low enough that the decrease in yellow dye density is slight, then the developing solution will not have adequate protection against aerial oxidation while if the amount of sulfite is increased to provide adequate protection against aerial oxidation, then the adverse effects on dye density will be severe and may reach unacceptable levels.
Other anti-oxidants, in addition to sulfites, which function to protect developing agents against aerial oxidation are known, and these can be used by themselves or in combination with a sulfite in photographic color developer compositions. For example, it is well known to use an hydroxylamine in a color developer composition to provide protection against aerial oxidation. Such use is described, for example, in U.S. Pat. Nos. 2,879,049, 3,462,269, 3,746,544 and 3,994,730. However, hydroxylamines are generally incapable of providing adequate protection against aerial oxidation when used as the sole anti-oxidant in color developer compositions that are subjected to conditions where aerial oxidation is a severe problem. As disclosed in U.S. Pat. No. 4,170,478, "Photographic Color Developer Compositions," by Nelson S. Case and Danny L. Wyatt, issued Oct. 9, 1979, particularly effective results are obtained by use of an hydroxylamine in combination with a member selected from the group consisting of alkanolamines which are free of carboxyl substitution, aliphatic monoamino monocarboxylic acids of up to three carbon atoms, and aminobenzoic acids.
It is toward the objective of providing an anti-oxidant which is highly effective in retarding aerial oxidation of primary aromatic amino color developing agents, when used either by itself or in combination with other anti-oxidants, and which, unlike sulfites, does not compete with couplers for oxidized developing agent, that the present invention is directed.